Easi Twist Jar Opener:
Does anyone actually carry any jars out when bushcrafting? That said, I once demonstrated how to use a large pickle jar as a kettle - but care has to be used to prevent it from shattering after removal from the fire. (No cold shocks)

At home, I use an elastic band on tight lids. Works every time for me, except ONCE on a never opened near antique jam jar...